Sizing of ethylene polymer structures



Patented Sept. 22, 1953 SIZING OF ETHYLENE POLYMER STRUCTURES ThomasFranklin Banigan, Kenmore, N. Y., assignor to E. I. du Pont de Nemoursand Company, Wilmington, Del., a corporation of Delaware No Drawing.Application September 13, 1951, Serial No. 246,526

Claims. (01. 117-1383) This invention relates to improvements in films,sheets, filaments, fibers, monofils and like structures of solidethylene polymer, and more particularly to improvements in the surfaceof ethylene polymer structures of high transparency.

Films of ethylene polymer (i. e., polyethylene) are highly useful in agreat variety of packaging applications such as for fresh produce,frozen foods, dried milk, chemicals and pharmaceuticals, textiles, etc.A description of films made from ethylene polymer is embodied in U. S.P. 2,219,700, issued to Perrin et a1. These films have excellentinherent moistureproofness, good mechanical strength and are highlyresistant to the action of many chemicals; and, though they aredescribed as being translucent to transparent, all ethylene polymerfilms heretofore commercially available have been translucent.Filaments, staple fibers, monofils and the like are described in U. S.P. 2,210,774.

Films, filaments, fibers, monofils, coatings, etc. of solid ethylenepolymer, however, have a propensity to develop strong W which make themdiflicult o manipulate during manufacture and subsequent processing,such as spinning, knitting, weaving, slitting, printing, sealing, etc.By reason of their highly charged surfaces, these articles alsoaccumulate heavy dust deposits which, of course, are very undesirable.

Further, ethylene. polymer films are smooth and very flexible; andsuperimposed sheets of the material separate with difliculty,particularly when pressure, even though moderate, is applied. Incontinuous roll form, the films do not slide easily over automaticpackaging machinery, resulting in very unsatisfactory operation.

Heretofore, a number of sizing compositions have been developed forimproving the surface properties of solid ethylene polymer structures,cf. U. S. P. 2,519,013 to T. F. Banigan, wherein is disclosed a sizingcomposition comprising a water-soluble alkyl aryl polyglycol ether.These sizing compositions are highly effieient as anti-static andslip-promoting agents for solid ethylene polymer structures such as thetranslucent film heretofore available. However, techniques have recentlybeen developed for producing commercially a transparent solid ethylenepolymer film; and it has been found that the sizing compositions whichhave previously been satisfactorily used for sizing translucent film areunsuitable for sizing transparent film, for the reason that in everyinstance the sizing composition does not improve both the slip andanti-static properties.

An object of this invention, therefore, is to improve the surfacecharacteristics of films, filaments, fibers, monofils, sheets, coatings,etc. of solid ethylene polymer whereby to enhance the slip thereof andto inhibit the accumulation of electrostatic charges thereon withoutdetracting from the transparency, flexibility, strength,moistureproofness, chemical resistance, heat sealability, etc. of theethylene polymer structures.

Another object is to provide novel compositions for improving thesurface characteristics of solid ethylene polymer structures, especiallyfilms, sheets and coatings. These and other objects will more clearlyappear hereinafter.

The above objects are accomplished according to the present invention bytreating the surfaces of a solid ethylene polymer structure with anextremely dilute aqueous composition consisting of water, dispersedpolyvinylacetate, a mixture of amine salts'of the formula,

wherein Alk is a primary saturated aliphatic hydrocarbon radical havingat least 6 carbon atoms; NX is an oxy-alkylene amine selected from thegroup consisting of the three ethanolamines, monoethanolmonomethylamine, ethanol dimethyl amine, diethanol-methylamine, andmorpholine; a: is an integer not greater than 2; and y is the differencebetween 3 and x; and, optionally, sodium chloride, thereafter removingexcess aqueous composition, and drying the treated structures.

The polyvinyl acetate particles deposited upon the film surface providefor good slip and excellent heat seals. It has been found that the typeand size of the polymer particle are relatively critical in providingfor good slip. For example, it has been found that the polymer particlesshould be as nearly spherical in shape as possible. Furthermore, theparticle must have an approximate particle size of at least 3 microns,but should not exceed 12 microns. Preferably, the amount of polyvinylacetate in the composition should be in the range of 0.10 to 2%, basedon the weight of water. Concentrations below the lower limits areineffectual for producing best results. On the other hand,concentrations of the dispersed polymer substantially greater than 2%result in the formation of a hazy coating which is highly undesirable incoating substantially transparent solid ethylene polymer film.

The mixed amine salts suitable for purposes of 3 this invention arefully described in copending application of McCarthy, Serial No.205,235, filed January 9', 1951. These mixed amine salts are thosewherein the amine portion is an oxy-alkylene amine, such as mono-, di-,and triethanol amine, the ethanol derivatives of the monoethyl anddimethyl amine, and morpholine. In other words, the group of agentsfound useful according to this invention are mixtures, composed ofcompounds defined by the general formula,

' (AlkO)-I"[O(NX)H] wherein a: designates the numeral 1 or 2; while 1/is the difference between 3 and m; Alk is a normal alkyl radical havingat least 6 carbon atoms; and NX represents an oxy-alkylene amineselected from the group consisting of the three ethanolamines, the threeethanol-methylamines (i. e., monoethanol monomethylamine, ethanoldimethylamine and diethanol-methylamine), and morpholine. The preferredmixture is an equimolecular mixture of monoalkyl-bis (diethanolamine)-phosphate and dialkylmono (diethanolamine) -phosphate, wherein thealkyl radical is a straight-chained, saturated, aliphatic primaryhydrocarbon radical of from 8-l6 carbon atoms, e. g., the hydrocarbonradical being derived by employing an equimolecular mixture ofn-octanol-l, n-decanol-l, and Lorol (a commercial mixture of primaryalcohols predominantly C12 and C14) in the preparation of the mixedamine salts. The concentration of these mixed salts in the compositionshould be within the range of 0.15% to 0.50%, based on the Weight of thewater.

Sodium chloride functions chiefly as an antiblocking agent; and itspresence, although not required, is preferred for this reason. Crystalsof the salt precipitate upon the film surface, and these crystalsfunction to separate adjacent film layers and, hence, preventfilm-to-film sticking. Sodium chloride crystals should be used in aconcentration within the range of 0.15 to 0.50 based on the weight ofthe water.

Application of the aqueous dispersion to the surface of the ethylenepolymer structure may be accomplished by any convenient expedient suchas by dipping, spraying, brushing, roll coating, etc., preferably at atemperature of from 60-70 C. Excess aqueous dispersion may be removed bysqueeze rolls, doctor knives, etc. The dispersion should be applied insuch amount that there will be deposited from to 25 milligrams of solidsper square yard of surface of the ethylene polymer structure.

The following examples will serve to further illustrate the principlesand practice of my invention. Parts and percentages are by weight unlessotherwise indicated.

Emample I Malt-extruded ethylene polymer film, 0.002 of an inch thick,having a haze value of 26 (transparent) was passed through an aqueousdispersion maintained at about 65 0. containing 0.50% particulatepolyvinyl acetate having a particle size of from 3-12 microns, 0.15% ofan equimolecular mixture of monoalkyl-bis (diethanolamine) -phosphateand dialkyl-mono (diethanolamine) -phosphate, wherein the alkyl radicalis a straight-chained, saturated, aliphatic, primary hydrocarbon radicalof from 8-16 carbon atoms, and 0.15% sodium chloride, all based on theweight of the water disperse medium. The dilute dispersion was preparedby adding small portions of more concentrated aqueous polyvinyl acetate(55-60% solids) to the proper amount of water. After passing through theaqueous dispersion, the film was passed between rubber squeeze rolls toremove the excess dispersion and dried. The resulting sized film was ofhigh clarity, and the haze value thereof did not differ substantiallyfrom that of the unsized film. In addition, the electrostatic propensityof the treated film at 75 F. and 35% R. H. (relative humidity) was 86volts, as compared with 560 volts for unsized film; and the coefficientof friction (film-to-film) at 75 F. and 75% R. H. was 0.55 (initial) and0.33 (running), as compared with 236+, both initial and running, forunsized film.

The electrostatic propensity characteristic of each film hereinafter setforth for purposes of comparison, was measured as follows:

A strip of film, 1 inch by 4 inches in size, is supported on and inelectrical contact with a fiat, slightly-roughened stainless steel platewhich is connected to a meter for measuring electrical potential, butwhich is otherwise insulated from its surroundings. The plate isroughened by rubbing it lightly with Carborundum cloth, making veryslight scratches at right angles to the direction of movement of thefilm. A weighted, felt-covered block which has a 1 inch by 2 inch facepresses the film into contact with the stainless steel plate. Anelectrostatic charge is generated by pulling the film for a distance of3 inches between the weighted block and the stainless steel plate, andthe charge so generated on the film discharges on to the stainless steelplate with which it is in contact and is measured by the meter. Thevalues registered on the meter (herein called electrostatic propensity)are purely relative and are useful only for purposes of comparison. Theyindicate the ability of a film to accumulate an electrostatic chargeunder the influence of friction normally encountered in manipulating orworking with the film.

The coefficient of friction of each film was determined as follows:

A rectangular plate of metal linked to an indicator is placed on top ofa sheet of polyethylene film supported on a smooth, flat surface. Thesheet is then pulled under the metal piece and over the supportingsurface at a steady rate. As the metal plate adheres to the moving film,it pulls on the indicator, the extent of the pull being in proportion tothe friction between the plate and film. The coefficient of friction issomewhat higher when the film is first pulled under the block (initial)than when it is running steadily (running). The metal block will give afilm-to-metal coefficient of friction; and when the block is wrapped inseveral layers of film and then tested, a film-to-film coefficient offriction is obtained.

Example II Following the procedure of Example I, film of the samespecifications was sized with an aqueous dispersion containing 0.50%polyvinyl acetate, 0.35% of an equimolecular mixture of monoalkyl-bis(diethanolamine) -phosphate and dialkyl mono (diethanolamine) phosphate,wherein the alkyl radical is a straight-chained, saturated, aliphatic,primary hydrocarbon radical of from 8-16 carbon atoms, and 0.15% sodiumchloride. The sized film was of high clarity; had an electrostaticpropensity of 62 volts at 75 F. and 35% R. H.; and the coefiicient offriction (film-to-film) at 75 F. and 75% R. H. was 0.76

(initial) and 0.50 (running), as compared with 236+, both initial andrunning, for unsized film.

In both of the foregoing examples, the heatsealing properties of theresultant film were excellent; and at heat-sealing temperatures rangingfrom 110 C.130 0., the seal strength was about 1500+ grams (see Ubben,U. S. P. 2,147,- 180).

It is to be understood that the sizing compositions of the presentinvention are not only satisfactory for substantially transparent solidethylene polymer film, but also for translucent films and solid ethylenepolymer in other forms. Furthermore, the sizing compositions of thepresent invention are an improvement over heretofore known sizingcompositions insofar as antistatic and slip-promoting properties areconcerned.

As many widely differing changes may be made without departing from thespirit and scope of my invention, it is to be further understood thatsaid invention is in nowise restricted save as set forth in the appendedclaims.

I claim:

1. Structures of ethylene polymer the surfaces of which have uniformlydistributed thereon a composition comprising essentially, particulatepolyvinyl acetate having a particle size of 3 to 12 microns, and amixture of compounds of the general formula,

wherein Alk is a primary saturated aliphatic hydrocarbon radical havingat least 6 carbon atoms; NX is an oxyalkylene amine selected from thegroup consisting of monoethanolamine, diethanolamine, triethanolamine,monoethanolmonomethylamine, ethanol-dimethylamine,diethanol-dimethylamine, and morpholine; a: is an integer not greaterthan 2; and y is the difference between 3 and x.

2. Structures of ethylene polymer the surfaces of which have uniformlydistributed thereon a composition consisting of sodium chloride,particulate polyvinyl acetate having a particle size of 3 to 12 microns,and a mixture of compounds of the general formula,

wherein Alk is a primary saturated aliphatic hydrocarbon radical havingat least 6 carbon atoms; NX is an oxyalkylene amine selected from thegroup consisting of monoethanolamine, diethanolamine, triethanolamine,monoethanolmonomethylamine, ethanol-dimethylamine,diethanol-dimethylamine, and morpholine; a: is an integer not greaterthan 2; and y is the difference between 3 and :r.

3. Films of ethylene polymer the surfaces of which have uniformlydistributed thereon a composition consisting of sodium chloride,particulate polyvinyl acetate having a particle size of 3 to 12 microns,and a mixture of compounds of the general formula,

wherein Alk is a primary saturated aliphatic hydrocarbon radical havingat least 6 carbon atoms; NX is an oxyalkylene amine selected from thegroup consisting of monoethanolamine, diethanolamine, triethanolamine,monoethanolmonomethylamine, ethanol-dimethylamine. di-

ethanol-dimethylamine, and morpholine; a: is an integer not greater than2; and y is the difference between 3 and x.

4. Transparent films of ethylene polymer the surfaces of which haveuniformly distributed thereon a composition consisting of sodiumchloride, particulate polyvinyl acetate having a particle size of 3 to12 microns, and a mixture of compounds of the general formula,

wherein Alk is a primary saturated aliphatic hydrocarbon radical havingat least 6 carbon atoms; NX is an oxyalkylene amine selected from thegroup consisting of monoethanolamine, diethanolamine, triethanolamine,monoethanolmonomethylamine, ethanol-dimethylamine,diethanol-dimethylamine, and morpholine; a: is an integer not greaterthan 2; and y is the difference between 3 and :c.

5. A method for improving the anti-static and slip characteristics ofstructures of ethylene polymer which comprises coating the surfaces ofsaid structures with a dilute aqueous dispersion containing from 0.1% to2% by weight, based on the weight of water, of dispersed particulatepolyvinyl acetate having a particle size of from 3-12 microns, and from0.15% to 0.50% of a mixture of compounds of the general formula,

wherein All: is a primary saturated aliphatic hydrocarbon radical havingat least 6 carbon atoms; NX is an oxyalkylene amine selected from thegroup consisting of monoethanolamine, diethanolamine, triethanolamine,monoethanolmonomethylamine, ethanol-dimethylamine,diethanol-dimethylamine, and morpholine; :c is an integer not greaterthan 2; and y is the difference between 3 and x, at a temperature of60-70 C., and thereafter drying said coated structures.

6. A method for improving the anti-static and slip characteristics ofstructures of ethylene polymer which comprises coating the surfaces ofsaid structures with a dilute aqueous dispersion containing from 0.15%to 0.50% by weight, based on the weight of water, of sodium chloride,from 0.10% to 2% of dispersed particulate polyvinyl acetate having aparticle size of from 3-12 microns, and from 0.15% to 0.50% of a mixtureof compounds of the general formula,

wherein Alk is a primary saturated aliphatic hydrocarbon radical havingat least 6 carbon atoms; NX is an oxy-alkylene amine selected from thegroup consisting of monoethanolamine, diethanolamine, triethanolamine,monoethanolmonomethylamine, ethanol-dimethylamine,diethanol-dimethylamine, and morpholine; a; is an integer not greaterthan 2; and y is the difference between 3 and :r, at a temperature of60-'70 C., and thereafter drying said coated structures.

7. The method of claim 6 wherein the structure is film.

8. The method of claim 6 wherein the structure is transparent film.

9. A sizing composition for enhancing antistatic characteristics and forpromoting slip characteristics of structures of ethylene polymers,comprising essentially water, from 0.10% to 2% by weight, based on theweight of water, of dispersed particulate polyvinyl acetate having aparticle size of from 3-12 microns, and from 0.15% to 0.50% of a mixtureof compounds of the general formula,

wherein Alk is a primary saturated aliphatic hydrocarbon radical havingat least 6 carbon atoms; NX is an oxy-alkylene amine selected from thegroup consisting of monoethanolamine, diethanolamine, triethanolamine,monoethanolmonomethylamine, ethanol-dimethylamine,diethanol-dimethylamine, and morpholine; a: is an integer not greaterthan 2; and y is the difference between 3 and as.

10. A sizing composition for enhancing antistatic characteristics andfor promoting slip characteristics of structures of ethylene polymers,comprising essentially water, from 0.15% to 0.50% by weight, based onthe weight of water, of sodium chloride, from 0.10% to 2% of dispersedparticulate polyvinyl acetate having a particle size of from 3-12microns, and from 0.15% to 0.50% of a mixture of compounds of thegeneral formula,

THOMAS FRANKLIN BANIGAN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,005,619 Graves June 18, 1935 2,279,501 Dickey et a1 Apr. 14,1942 2,279,502 Dickey et a1 Apr. 14, 194% 2,413,428 Billings Dec. 31,1946

5. A METHOD FOR IMPROVING THE ANTI-STATIC AND SLIP CHARACTERISTICS OFSTRUCTURES OF ETHYLENE POLYMER WHICH COMPRISES COATING THE SURFACES OFSAID STRUCTURES WITH A DILUTE AQUEOUS DISPERSION CONTAINING FROM 0.1% TO2% BY WEIGHT, BASED ON THE WEIGHT OF WATER, OF DISPERSED PARTICULATEPOLYVINYL ACETATE HAVING A PARTICLE SIZE OF FROM 3-12 MICRONS, AND FROM0.15% TO 0.50% OF A MIXTURE OF COMPOUNDS OF THE GENERAL FORMULA,